Then what else besides the silencer is there ?
Oh dear lookout, I like you, I really do but your lack of understanding of all the evidence is appalling. For the millionth time, Jeremy's guilt is derived from Sheila's innocence, it's as simple as that.
And for the benefit of any new reader who hasn't a clue, the evidence shows that only Jeremy or Sheila had the opportunity to murder the family, an outsider acting a lone without any help from Jeremy is a non starter. In fact, had Jeremy set it all up for a third party he would have made bloody sure he had a bulletproof (sos) alibi! Yet another factor which points to Jeremy being present when the dirty deeds were done.
Then there are the other acquaintances with very convenient bulletproof alibis.